1. Field of Invention
The present invention relates generally to a semiconductor device and a method for manufacturing the same, and more particularly, to an MOSFET (metal oxide semiconductor field effect transistor) structure with a channel region of high mobility and a method for manufacturing the same.
2. Description of Prior Art
One trend of the integrated circuit technology is to integrate as many MOSFETs as possible in a unit area of a chip. With scaling down of the MOSFET dimensions, a gate length is reduced to less than 32 nm. However, due to the reduced gate length, the gate has a poor controllability on a channel region, which degrades properties of the MOSFET, especially causes a short channel effect in which a threshold voltage of the MOSFET decreases. Moreover, a poor conductivity of polysilicon causes a voltage drop across a polysilicon gate when a voltage is applied to the gate. Thus, an actual gate voltage applied to the channel region is further reduced.
A dual-gate device or an ultra-thin SOI device can enhance controllability of the gate on the channel region, and thus suppresses the short channel effect.
Another trend is to replace the polysilicon gate with a metal gate, which alleviates an unfavorable effect of polysilicon depletion by using a metal having a good conductivity. In manufacturing such a semiconductor device, a replacement gate process is typically used to precisely control a gate length, which comprises the steps of forming a dummy gate conductor such as polysilicon, selectively removing the dummy gate conductor to provide a gate opening, and finally depositing a gate metal in the gate opening. An MOS device manufactured by the replacement gate process enhances controllability of the gate on the channel region.
However, the above novel devices, such as the dual-gate device, the ultra-thin SOI device, and the MOS device having a metal gate, still use conventional channel materials, which limits maximum values of an output current and an operating frequency, and has no improvement in a power consumption.